Images of police dousing students with pepper spray at UC Davis and jabbing them with batons at UC Berkeley drew national condemnation and set off new protests Monday, as UC’s president urged chancellors across the state to protect students’ right to protest peacefully.

The confrontations have led to soul-searching across the UC system and calls for UC Davis’ chancellor to resign, extraordinary developments at college campuses that pride themselves on a history of activism and political dissent.

“We cannot let this happen again,” UC President Mark Yudof said, after convening chancellors to discuss the use of police force, which gained national attention after video of an officer pepper spraying a row of sitting students, their arms locked in peaceful resistance, spread across the Web.

At a rally at UC Davis, Chancellor Linda Katehi took the stage and said, “I’m here to apologize” for the pepper spraying. “I really feel horrible for what happened on Friday.”

She spoke only briefly, then students shouted at her to step down. A petition calling for her resignation had received more than 70,000 online signatures by Monday afternoon. By 5 p.m., students returned to the quad and began erecting a dozen tents to restore the Occupy encampment.

Police force galvanized further protests at some UC campuses Monday and has been criticized in a range of forums such as “The Colbert Report” and Forbes.com.